In recent years, a diesel engine has been widely equipped with a diesel particulate filter (DPF) in an exhaust system (e.g. muffler) and particulates contained in exhaust gas are removed by the DPF. The DPF is formed into a shape such as cylinder or elliptical cylinder corresponding to a muffler shape for a diesel engine by bonding sintered segments formed of silicon carbide or the like using a bonding material. The segments are formed to have a rectangular or square tubular shape, and are arranged and bonded in rows. The bonded body is ground into a cylindrical shape or the like to have a shape corresponding to the muffler shape.
The DPF is incorporated into a muffler using a press tool. It is preferable that the DPF be pushed into the muffler without being inclined, from the viewpoint of exhaust gas leakage prevention, mounting stability, and the like. This requires that the degree of flatness and the degree of parallelism of the end face be within a specific allowable range. However, since the segment is formed of a sintered product, the length of the segment tends to vary. Moreover, since the bonding material may protrude from the end face, the end face of the DPF becomes uneven, whereby a product having a shape outside the allowable range may be produced. Therefore, it is necessary to measure the shape of the DPF in order to select only a DPF having a shape within the allowable range. In related art, the shape of the DPF is measured by the following method.
(1) A number of probes (e.g. dial gauge or linear gauge) are disposed corresponding to respective segments and caused to contact the end faces of the segments at the same time to measure the heights of the segments.
(2) One probe (e.g. dial gauge or linear gauge) is provided, and the worker measures the data of the end face while rotating the DPF.
(3) The DPF is provided on a turntable, and the edge of the DPF is detected using an image sensor while rotating the DPF to measure the height of the perimeter of the DPF (see patent document 1).
Patent document 1: JP-A-55-37918